CN202631617U - Output-stage over-current detection circuit - Google Patents

Abstract

Disclosed in the utility model is an output-stage over-current detection circuit that comprises a selector and an overcurrent comparator. The input terminals of the selector are connected with conduction voltage drop positions and drive signals; and the selector carries out sampling on the conduction voltage drop of the conducted output tube at the output stage according to the drive signal at the output stage. And the output terminal of the overcurrent comparator is respectively connected with the output and a preset value of the selector; and the conduction voltage drop is compared with the preset value and whether the over-current phenomenon occurs at the output stage can be determined so as to realize over-current detection. According to the utility model, the disclosed circuit has advantages of the capability of continuous detection of currents with inductive loads, low cost and high integration level.

Description

A kind of output stage over-current detection circuit

Technical field

The utility model relates to a kind of output stage over-current detection circuit, is applicable to the H bridge-type output stage that drives inductive load, like motor drive circuit.

Background technology

The common way of output stage over-current detection is to be connected on the power rail with sampling resistor, and electric current can produce a voltage that is directly proportional with electric current through sampling resistor.Carry out current sample through detecting this voltage.

Then can bring problem but this way is used on the H bridge-type output stage that is applied in the driving inductive load, as shown in Figure 1, the output of H bridge is made up of 4 switching tubes.Current limliting detects and relies on sampling resistor 407 to accomplish.The output current limiting value is by the input VR decision of sampling resistor 407 and comparer 408.

Suppose that when beginning, inductive load 411 electric currents are zero, 401 and 403 conductings, drive inductive load 411 this moment, and its electric current constantly increases, and the voltage at resistance 407 two ends is constantly increase also, when this voltage reaches VCC-VR, promptly thinks the generation overcurrent.This moment, the comparer output switching activity turn-offed 401 through controller 409 and driver 410, and output gets into the afterflow state.The electric current of inductive load 411 carries out afterflow through diode 405 and 403, after a fixing time-delay, finishes the afterflow state, returns driving condition, 401 conductings once more.Constant like initial conditions, then can repeat this circulation always.

Notice that when afterflow takes place the electric current on the resistance 407 is zero, after therefore protecting, can't continue to monitor the size of current of inductive load.Therefore must rely on circuit that fixing time of afterflow is set,, return driving condition through after this time.In some applications, in when switching-over, its induced electromotive force is bigger like motor, and current attenuation gets very slowly in the time of can making afterflow, and electric current increases very soon during conducting.In this case, if turn off delay time is bigger, then output remains driving condition in turn off delay time, and it is very fast that electric current increases; Current attenuation must be slower in the fixing turn-off time, so just can not guarantee current attenuation to setting value, and after returning the driving attitude electric current that surpasses setting value is further increased.It is thus clear that this output current limiting framework can't guarantee rational time of afterflow, its basic reason is because over-current detection circuit can't continue to detect the electric current in the load when afterflow.

And sampling resistor 407 is generally the low resistance precision resister, and its cost is higher, and because the requirement of its precision is difficult for being integrated into IC inside.

In order to address the above problem, the inventor designs a kind of output stage over-current detection circuit, and this case produces thus.

The utility model content

The utility model provides a kind of output stage over-current detection circuit in order to overcome the deficiency of prior art, is applicable to the H bridge-type output stage that drives inductive load, like motor drive circuit.

In order to achieve the above object, the utility model is realized through following technical scheme:

A kind of output stage over-current detection circuit,

Comprise a selector switch, its input end connects conduction voltage drop and drive signal, according to the drive signal of output stage the conduction voltage drop of the efferent duct of conducting in the output stage is sampled;

Comprise an overcurrent comparer, its input end connects the output and a preset value of selector switch respectively, and conduction voltage drop and preset value are compared, and judges whether overcurrent of output stage, realizes over-current detection.

Having the following advantages of the utility model: electric current that can the continuous detecting inductive load, and cost is low, and integrated level is high.

Description of drawings

Fig. 1 is applied to the circuit diagram of H bridge-type output stage for prior art;

Fig. 2 is the circuit diagram of the utility model preferred embodiment;

Fig. 3 is applied to the circuit diagram of H bridge-type output stage for the utility model preferred embodiment.

Embodiment

In order to make those skilled in the art person better understand the utility model scheme, will combine accompanying drawing below, the technical scheme among the utility model embodiment is carried out clear, complete description.

As shown in Figure 2, a kind of output stage over-current detection circuit comprises selector switch 1, overcurrent comparer 2.Four input ends of selector switch 1 connect conduction voltage drop 1, conduction voltage drop 2, drive signal 1, drive signal 2 respectively, according to the drive signal of output stage the conduction voltage drop of the efferent duct of conducting in the output stage are sampled.The input end of overcurrent comparer 2 connects the output and a preset value VR of selector switch 1 respectively, and conduction voltage drop and preset value VR are compared, and judges whether overcurrent of output stage, realizes over-current detection.

As shown in Figure 3, the output of H bridge is made up of 4 switching tubes.Selector switch 1 selects corresponding saturation voltage drop to export to overcurrent comparer 2 according to the drive signal of NPN pipe efferent duct 507 and 510.Overcurrent comparer 2 compares the output and a preset value VR of selector switch.The output current limiting value is by the IV characteristic and the preset value VR decision of efferent duct 507 and 510.

When supposing beginning, inductive load 511 electric currents are zero, efferent duct 505 and 510 conductings, and drive inductive load 511 this moment, and its electric current constantly increases, and the conduction voltage drop of efferent duct 510 increases thereupon.The input SEL1 of selector switch 1 and SEL2 are respectively the base signal of efferent duct 510 and 507, and when efferent duct 510 conductings, selector switch 1 passes to overcurrent comparer 2 with the conduction voltage drop of efferent duct 510, and VR compares with setting value.When the conduction voltage drop of efferent duct 510 reached VR, the output overcurrent signal of overcurrent comparer 2 turn-offed efferent duct 505 through controller 503 and driver 504, accomplishes over-current detection.Output then gets into the afterflow state, and the electric current of inductive load carries out afterflow through diode 508 and efferent duct 510.

Can make over-current detection have lagging characteristics through the sluggishness of setting VR.When output gets into the afterflow state, can set the condition that output stage is got back to driving condition through VR is reduced a hysteresis voltage VH.The electric current of inductive load 511 constantly descends during the afterflow attitude, and the conduction voltage drop of efferent duct 510 also descends thereupon; When its conduction voltage drop dropped to VR-VH, overcurrent comparer 2 is the output overcurrent signal no longer, and controller and driver are opened efferent duct 505 again, return driving condition.If voltage and loading condition are constant, then the output meeting is constantly switched between afterflow and driving condition, makes the saturation voltage drop of managing down between VR and VR-VH, and the Current Control of guaranteeing inductive load is in preset scope.

From said process, can find,, the lagging characteristics of current-limiting circuit so just can be set freely because the change of current sample mode in this patent has realized the continuous detecting load current.After overcurrent took place, the duration of afterflow state was depended on the sluggish size and the speed of current attenuation.If current attenuation is slower, then the duration is longer; Otherwise current attenuation is very fast, and then the duration is shorter.Therefore use the current-limiting circuit of this patent to have rational time of afterflow, and its current ripples can set, solve insurmountable problem under framework described in the background technology.

Owing to use the conduction voltage drop of efferent duct to come current limliting, therefore need not examine leakage resistance, practiced thrift cost.

In sum, the utlity model has following advantage: electric current that can the continuous detecting inductive load, and cost is low, and integrated level is high.

The above only is the preferred embodiment of the utility model, is not to any pro forma restriction of present embodiment.Anyly be familiar with those skilled in the art; Do not breaking away under the utility model technical scheme scope situation; Can utilize the method and the technology contents of above-mentioned announcement that the utility model is made many possible changes and modification; Perhaps be revised as the equivalent embodiment of equivalent variations, all still belong in the scope of the utility model protection.

Claims (1)

1. output stage over-current detection circuit is characterized in that:

Comprise a selector switch, its input end connects conduction voltage drop and drive signal, according to the drive signal of output stage the conduction voltage drop of the efferent duct of conducting in the output stage is sampled;

Comprise an overcurrent comparer, its input end connects the output and a preset value of selector switch respectively, and conduction voltage drop and preset value are compared, and judges whether overcurrent of output stage, realizes over-current detection.

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